Numerous processes are within the purview of those skilled in the art for forming toners. Emulsion aggregation (EA) is one such method. EA toners are generally formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex emulsion by first forming a seed polymer. Other methods of emulsion/aggregation/coalescing for preparing toners are illustrated in U.S. Pat. Nos. 3,644,263; 3,879,327; 4,243,566; 5,403,693; 5,418,108; 5,364,729; 5,346,797; 5,527,658; 5,585,215; 5,650,255; 5,650,256; 5,501,935; 7,683,142; 7,977,024; 8,124,309; 8,163,459; and 8,168,699, the disclosures of which are hereby incorporated by reference in their entirety
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins. The incorporation of these polyester resins into toner requires that the resins first be formulated into emulsions prepared by solvent containing batch processes, for example solvent-based phase inversion emulsification (PIE). PIE is currently the main process of forming emulsified polyester resin latex for use in polyester emulsion aggregation toners. Ammonium hydroxide (NH4OH) is commonly used as a “basic neutralization agent” in the polyester emulsification process. The ammonium hydroxide inverts the resin dissolved oil phase (resin/solvent solution) in water to form a stable aqueous emulsion.
In the PIE process, the type of base or neutralizing agent and ratio of neutralizing agent to resin or solvent plays a very critical role. There are many input process parameters such as resin composition, resin molecular weight and acid value that can vary which make it difficult to emulsify high molecular weight branched amorphous polyester resins to produce the desired particle size range (e.g., 100-250 nm) and a narrow particle size distribution. Lot-to-lot variations of resin acid value, viscosity, and resin softening point requires adjustments in the PIE process parameters such as neutralization ratio and solvent ratio to achieve the desired toner particle size. Determining such adjustments is time-consuming and requires much trial and error to identify the exact conditions that will allow a resin lot to be successfully emulsified. Moreover, even with these modifications some polyester resins are not successfully emulsified with failed batches.
It would thus be advantageous to identify a new process which can consistently provide the desired particle size without batch-to-batch variations.